1. Field of the Invention
This invention pertains to single and multiple arrangements of porous media barrier or impingement type air filter units which are removable from a top wall of the filter cabinet and are provided with improved reverse or backflushing air filter cleaning systems to provide for operation of the filter system at air flow rates greater than the derated systems heretofore required.
2. Background
In the art of porous media impingement type air filters and dust collectors the development of so called reverse jet or backflushing type filter cleaning systems has complicated the arrangement of air filter units and their support cabinetry or housings. The reverse jet nozzles and valving as well as the manifolding therefor must be removed or set aside to gain access to the filter element or the filter element must be removed from the bottom of its support housing. Both situations are disadvantageous in that the removal of the backflushing structure is difficult and complicates the support equipment for this mechanism. Access to the filter element through the side or bottom of a filter housing is particularly disadvantageous in that it requires entry into the so called "dirty" side of the interior of the filter housing.
Another problem associated with the conventional arrangements of pleated paper or similar types of porous media filter elements with respect to reverse jet type filter cleaning systems pertains to the fact that the reverse jet air flow develops a pressure pulse having a gradient which tends to propel particulate material off and away from the filter element in such a way that the material having the greatest distance to fall into a collection chamber is not propelled away from the filter element sufficiently to prevent it from being entrained in the air flow stream through the filter element and recollecting almost immediately on the element itself. This practice as well as other problems with prior art filters has necessitated the substantial derating of filter elements used with reverse jet air cleaning or flushing systems.
Yet another problem associated with prior art type air filters pertains to certain applications of material separation processes wherein the particulate material being separated from the process air has a relatively high moisture content. In conventional filter construction this moisture content tends to cause the separated material to collect on the wall of the lower portion of the filter housing and in freezing conditions results in a substantial buildup of material within the filter housing which cannot be dislodged except by entry into the interior of the housing and thereby requiring shutdown of the filter system. Moreover, water vapor condensation often occurs in the reverse flushing air control circuit and in conventional arrangements can freeze in the control valves and conduits thereby causing the reverse jet flushing air system to malfunction.
Accordingly, there have been several problems in the art of porous media impingement or barrier type filter units which are utilized in a wide variety of applications, which problems have not been overcome with known types of filter structures. The conventional way of constructing the filter cabinet, the reverse jet flushing air system, and providing access to the filter elements has continued to present problems in non uniform loading of the filter elements, non uniform and inefficient cleaning of the elements, poor access to the elements for replacement or repair and poor control over the discharge of separated material. These and other disadvantages of prior art filter systems have been overcome with the air filter systems of the present invention.